Gas heated rotary drier

ABSTRACT

A gas drier for tobacco and the like having a rotatable drum with internally disposed axially extending V-shaped vanes each open to the gas burners disposed along the bottom of the drier.

United States Patent [1 1 Neville Feb. 18, 1975 I GAS HEATED ROTARYDRIER [75] Inventor: Richard E. G. Neville, Salisbury,

England [73] Assignee: AMF Incorporated, White Plains,

122 Filed: July 16, 1973 21 App1.No.;379,743

[30] Foreign Application Priority Data July 21,1972 Great Britain..34291/72 US. Cl 34/133, 34/134,432/107 [51] lm. C1 F26b 11/02.

Field of Search 34/134, 133. 139; 432/107. 432/112; 165/89; 259/89, 90

[56] References Cited UNITED STATES PATENTS 2.348,6 73 5/1943 Degner 4321;

be N e T L/l/l/Y/l/f 2,639,133 5/1953 Clary 432/113 FOREIGN PATENTS ORAPPLICATIONS 10,744

Primary Examiner-Kenneth W. Sprague Assistant Examiner-Larry 1. SchwartzAttorney, Agent, or FirmGeorge W. Price; Charles J. Worth 57 ABSTRACT Agas drier for tobacco and the like having a rotatable drum withinternally disposed axially extending V- shaped vanes each open to thegas burners disposed along the bottom of the drier.

8 Claims, 7 Drawing Figures Vl/I/l/l/i/jY/jA/ 5/1895 Great Britain432/113 SHEET U 0F 4 1 GAS HEATED ROTARY DRIER This invention relates todriers for particulate or loose material such as rag or stem tobacco.

With the general availability of natural or propane gas, the gas drieris a relatively inexpensive and attractive alternative to the'steamdrier for rag or stem drying. With a low thermal capacity and rapidresponse it is particularly suitable for automatic moisture control.

A known drier traditionally used for stem drying comprises a rotatablymounted cylinder having radially inwardly extending paddles. Thecylinder is heated by strip type burners arranged below and parallel tothe cylinder axis to throw flame at the cylinder along its entire lengthat the same moment. lts short paddles and high cylinder temperaturessuit the low flow/high moisture removal stem application. The heatconduction along the paddles is negligible and size is based on thecylinder heating surface only.

For rag drying, larger paddles are required to match the larger volumeflow. To keep the size and dwell time of the drier comparable to that ofa steam drier for the same working temperatures (or smaller for higherworking temperatures) the paddles must supply heat to the tobacco.

Conducting paddles are not practicable. Using the best practicalconductor, copper, a 1 inch base triangular section only barely conductssufficient heat; combined with an ne-half inch cylinder thickness thethermal capacity of the whole would be totally unacceptable. Theconduction of steel is about'eight times worse and stainless 24 timesworse. 1

According to the invention there is provided a rotary drier forparticulate or loose material comprising a cyl-v inder arranged torotate about its axis disposed horizontally or inclined to thehorizontal and having formed along its cylindrical surface a pluralityof hollow paddles extending axially along said cylinder and inwardlythereof. The interior of said paddles communicate with the exterior ofthe cylinder and at least one gas burner arranged below the cylinder todirect flame into the interior of the hollow paddles.

In the present drier the paddles are heated directly by gas flame,giving the maximum heat transfer and ensuring a high thermal efficiency.The paddles are preferably ofa V-shape or hollow triangular sectionseach with an open base exposed to the combustion space. If strip burnersparallel to the cylinder axis are used there would be no room for thecooled gases in he paddle to escape, which would consequently preventthe flame entering the hollow paddle. The present construction avoidsthis problem by, in effect, dividing the normal strip type burner intoshort lengths which are inclined to the cylinder axis. Accordingly, atany one moment the flame only enters the paddle at the intersections ofthe open paddle base and the inclined burners. This arrangement allowsthe flame to enter the hollow paddle the detailed description whichfollows, taken together with the accompanying drawings wherein severalembodiments of the invention are illustrated by way of example. It is tobe expressly understood, however, that the drawings are for illustrationpurposes only and are not to be construed as defining the limits of theinvention.

FIG. 1 is a side view of the rotary drier,

FIG. 2 is a view of the drier at the feed end thereof,

FIG. 3 is a view on the delivery end of the drier FIG. 4 is a sectiontaken along the line 4-4 in FIG.

FIG. 5 is a plan view of the burners taken in the direction of thearrows 55 in FIG. 1,

FIG. 6 is a scrap view of an expansion follower for temperaturemeasurement, and

FIG. 7 is a side view of a rotary drier which includes an air inletprobe for suppressing exhaust air ventilation.

Referring now to the drawings, a drier in accordance with the inventionis provided with a chasis l0 comprising longitudinal side channels 11supported on legs 12 and having cross channels 13. On the cross channels13 are mounted pairs of support rollers 14, preferably of a reinforcedphenolic resin which carry a cylinder 15 byway of track rings 16 and 17attached by spacers. The cylinder 15 is driven by belts 18 passingaround a belt ring, formed as part ofthe track ring 16, and driven by ageared motor 19 or the like. The cylinder has its axis of rotationdisposed at an angle of l% or 35? according to the desired flow rate anddrying capacity. Generally, the inclination is preferably between 1 and5. A thrust roller 20 is mounted on the cross channel 13 at the feed endfor engagement with a rim 21 provided on the cylinder 15. A feedconveyor 47 which may be of the vibratory type is provided at one end ofthe drier with a discharge chute 55 being provided at the other end.

As is seen from FIG. 4, the cylinder 15 is formed with a series ofinwardly projecting paddles 24 which are generally V-shaped or of anopen base triangular cross section all extending axially off thecylinder. One side of each paddle 24 is positioned radially and theother obliquely relative to the rotation axis of the cylinder 15.

This is to insure that the radial sides of paddles 24 BURNER EQUIPMENTNormally forced draught ribbon type gas burners are fitted, with pilotburners, flame failure control and pneumatically operated-modulatingvalve giving a 20:1 turn down range. The burner assembly (see FIG. 5) ispivotably mounted on an axis adjacent and parallel to by leaving spaceeither side of the scouring out of a chassis side member so that it canbe swung down for cooled gases, and insures uniform heating of thecylinder throughout its length.

Further features of the presentinvention are cylinder temperaturecontrol by cylinder expansion measurement, or differential or zonalcylinder temperature control by thermistor, and combined casing coolerand airaccess to the burners. Heating by diagonal strip burners has thefollowing advantages compared with other known methods, viz.

I. It is simple and avoids the use of a fan found in other driers whichhas to handle very hot gasses, 2. The cylinder and especially its openpaddles can be uniformly heated from end to end, or 3. The cylinder andespecially its open paddles can be heated differentially to reduce theoverdried tobacco at start-up and shut-down and to give quick responsecontrol during normal running,

4. Direct flame exposure of the open paddles gives a more efficient heattransfer from gas to cylinder.

The hot combustion gases are kept in close proximity to the cylinder bya cylindrical combustion space casing 27, (see FIG. 4) which isconcentric with the cylinder l5 and surrounds it at a few inchesdistance. The bottom of the casing'27 is open for the burners 28 and thetop includes a tapered flue gas collection manifold 29 which connects toa flue duct 30.

A few inches outside the combustion space casing 27 are two furtherconcentric curved sheets 31 and 32, one on each side of the cylinder 15,forming a narrow curved air passage way. The passage way finishes eitherside of the flue manifold where a thin slot 33 connects with the cornerspace 35 formed by the outer insulation boards 34.

Both corner spaces 35 are connected to a fan 36 (see FIG. 1) whichenables air to be drawn up through the curved passage way, heated anddelivered to the cylinder via a ducting 37. Ambient air is drawn inthrough an adjustable entry 39. This method of pre-heating the cylinderdrying air has the double purpose of improving the overall thermalefficiency of the drier and considerably reducing the heat conducted tothe outer insulation. As a result the outside surface of the insulationis below 100F. and typically only 20F. above ambient. The outer casingis of conventional asbestos board construction.

Alternatively, where pre-heating of the drying air is not required, thecorner spaces are connected to the combustion gas flue 29 and a flow ofcasing cooling air induced by convection.

EXHAUST AIR For high duty application the drying air is contra flow andthe cylinder is provided with a cylindrical feed end sieve 40 as anextension of the cylinder 15, and a sieve cleaner 41. Contra flow isessential for applications with high input moisture content where theexhaust air I is saturated. Additional air is fed via fan inlet 57 tothe feed hood from a pre-heater in such applications to preventcondensation.

For lesser duties a lower volume air flow is used without a sieve.

Proposed Range of sizes Cylinder diameter in feet 3 4 Number of paddles4 8 cylinder rotational 8 speed in r.p.m.

Maximum rag flow rate at:

3% cylinder inclination in lb/hr 5.000 10.000 20,000 F34" cylinderinclination in lb/hr 2.500 5.000 l0,000

Heated cylinder lengths in feet: 8

l2 l2 l6 l6 I6 20 20 24 directed toward the working radial surfaces ofthe paddles 24.

This direct heating of the paddles 24 permits a thin cylinder and paddlewall to be used, giving a lower thermal capacity than the correspondingsize of steam drier. Typical heating and cooling rates for a oneeighthinch thick cylinder being 50F/min under normal working conditions. At 15r.p.m. this is a fluctuation of only 3VaF per revolution.

CYLINDER TEMPERATURE CONTROL The traditional gas control from thecylinder exhaust air temperature is not satisfactory for use withautomatic moisture control system or for good manual control. Theexhaust air temperature is only a poor reflection of the cylindertemperature as it is effected by exhaust air flow, tobacco temperatureand moisture removal and it furthermore lags behind the cylindertemperature.

For manual control and the simpler automatic control systems, the gasdrier of the present invention is fitted with average cylindertemperature control by measurement of cylinder expansion using followers42 (see FIG. 6) on one but preferably on both runner track rings 16 (notshown) and 17. The position of a follower 42 is converted by atransducer 43 into van electric signal and the difference between thesignals from the transducers 43, after smoothing, gives a measure ofcylinder expansion and hence cylinder temperature.

The resulting signal is fed to a temperature indicating processcontroller (not shown) which controls a modulating valve 44 in the gassupply to maintain a set temperature. With automatic moisture controlthe set point of the temperature is adjusted automatically by cascadecontrol.

THE CYLINDER TEMPERATURE IS SET MANUALLY The virtually instantaneousreaction to cylinder temperature results in a very tight control ofcylinder temperature. The burners are sized to give double the normalworking heat. This, combined with the low thermal capacity of thecylinder, enables the cylinder tempera ture to be increased or reducedrapidly and accurately within the normal working range of l50to 400F.

An over-riding safety control is fitted based on the conventionalexhaust air temperature measurement.

ZONAL CYLINDER TEMPERATURE CONTROL For applications with fully automaticfeed forward and feed back control from moisture meters with automaticstart-up and shut down the burner 28 is divided into two or moresections (see FIG. 5) depending on the length of the drier. Each sectionhas an independent gas control valve (not shown).

The temperature of each zone of the drier corresponding to each burnersection is measured by a number of thermistors 56 (of which only one isshown in FIG. 1) fixed to the cylinder surface and connected in parallelto give an average temperature for each zone.

This replaces the overall cylinder expansion measure-.

ment used for manual and simpler automatic control systems.

One side of each thermistor is connected to the cylinder and connectionis made to the rotating cylinder by a sprung metal roller on the trackring.

The other connection from the thermistors in each zone is brought to aslip ring mounted on an insulated extension of the track ring.Thermistors are used for the temperature measurement as their very highresistance change with temperature makes them insensitive to variationin slip ring resistance. Instead of arranging slip rings on the outsideof the cylinder the connections may extend to one end of the cylinderwhere longitudinally extending arms are provided with a connected armdiametrically positioned, at the centre of which arm is mounted a slipring of considerably less diameter than that of the cylinder. Since asmall diameter slip ring can be used in such a construction aproprietory slip ring and brush enclosed in a dustproof housing can beused.

A separate temperature controller for each zone enables the temperatureof each zone to be controlled independently of its neighbor. This zonalor differental temperature control is used at start up and shut down andalso during normal running.

At start up as the tobacco runs in from the infeed 47 to the discharge55, the down stream zones are heated up successively after the upstreamzones using a programmed start. Similarly at shut down as the tobaccoruns out the upstream zones are turned off successively before the downstream zones. This avoids over-dried tobacco during run-in and run-out.

During normal working the feed end zone only is used to control shortterm variations in output moisture control and the delivery end zone iscorrect short term output variations in mositure content. This isachieved by a system of duel control which ensures that short termfluctuations are corrected by the appropriate end zones and long termvariations are corrected by the general temperature level of all zones.

This arrangement of zonal cylinder temperature control enables quickresponse corrections to be made which are not possible with acylinderofa uniform temperature throughout its length. The Paddles aredivided between zones to allow for any differential expansion.

To improve the ability of the tobacco to fill cigarettes using a minimumamount of tobacco, it is often required to stew the tobacco in thedrier, i.e., suppress the exhaust air ventilation and raise thetobacco'to around 170F. The heat for drying is supplied by the drier andthough the majority of the moisture removal still takes place in thedrier, a greater proportion is removed in the cooler by evaporativecooling.

A weakness of this method of operation is the uneven moisture loss thatcan occur at this high temperature both between the drier and cooler andin the cooler. To overcome this there is provided a pre-heated air inletprobe 45 as shown in FIG. 7.

This probe 45 is introduced at the delivery end of the drier anddischarges air via an air diffuser 46 about one-third of the heat lengthfrom the delivery end. The feed-end of the cylinder is carefully sealedand the tunnel of the vibrating feed conveyor 47 is sealed by asuccession of curtain seals (not shown). A small controlled amount ofair (approximately 250 c.f.m. in a 4 ft. diameter drier) is exhaustedfrom the feed hood. Adjustment of this air flow determines thetemperature achieved by the tobacco in'the first two-thirds of thecylinder heated length. The tobacco temperature at this point is sensedby a thermistor 48 attached to the end of the probe and so arranged thatit is always covered with a fresh fall of tobacco.

The majority of the air (approximately 1,250 c.f.m. in a 4 ft. diameterdrier) is exhausted from the deliver end hood so that the ventilationwhich takes place in the last one-third of the cylinder heated lengthcools the tobacco to normal drier outlet temperature of around l00/120F.

The air inlet probe 45 is cantilevered from the delivery end andarranged to rotate to keep it clear of falling tobacco. The probe isrotated through a shaft 49 driven by a motor 50. The hot air from thecurved air space and the slots 33 is fed to the probe by a fan 51 andducting 52. Ambient air enters through an adjustable entry 53. Thethermistor connections are brought out via a small slip ring (notshown). The air diffuser has sufficient pressure drop across it toprevent tobacco settling on it.

The drying capacity of the first two-thirds of the drier length isreduced due to the suppressed ventilation. In a 4' dia. X 16 heatedlength cylinder of the kind (shown in FIG. 7) up to 5 percent moisturefrom 5,000 lbs/hr. of rag can be removed. This removal figure includesthe removal in the cooler, the heat for which is supplied in the drier.

Although several embodiments of the invention have been illustrated anddescribed in detail, it is to be expressly understood that the inventionis not limited thereto. Various changes may be made in the design andarrangement of the parts without departing from the spirit and scope ofthe invention as the same will now be understood by those skilled in theart.

I claim:

1. A rotary drier for, particulate or loose material comprising acylinder arranged to rotate about its axis inclined to the horizontal,said cylinder having formed along its cylindrical surface a plurality ofhollow paddles extending axially along said cylinder and inwardlythereof, said paddles being V-shaped in cross section with one side ofeach paddle being disposed radially and the other side being disposedobliquely thereto, the interior of said paddles communicating with theexterior of the cylinder andat least one gas burner arranged below thecylinder to direct flame into the interior of the hollow paddles.

2. A rotary drier as claimed in claim 1 in which said burner comprises aplurality of strip burners which are provided positioned obliquely withrespect to the cylinder axis.

3. A rotary drier as claimed in claim 1 in which said cylinder issurrounded along its length by a cylindrical wall defining a combustionspace between said cylinder and said wall, the interior of said paddlescommunicating with said combustion space, and the bottom of thecombustion space being open to said burner.

4. A rotary drier as claimed in claim 3 in which the top of thecombustion space includes a tapered flue gas collection manifold whichcommunicates with a flue duct for removing waste combustion gases.

5. A rotary drier as claimed in claim 4 further including means forintroducing air into said cylinder, said means comprising a passage wayfor conducting ambient air around said cylinder to preheat the air andfor separating the ambient air from combustion gases, a fan for drawingair through said passage way and ducting for passing the preheated airto the interior of said cylinder.

6. A rotary drier as claimed in claim further including an inlet probefor introducing pre-heated air into said cylinder at a positionintermediate its ends.

7. A rotary drier for particulate or loose material comprising acylinder arranged to rotate about its axis inclined to the horizontal,said cylinder having formed along its cylindrical surface a plurality ofhollow paddles extending axially along said cylinder and inwardlythereof, the interior of said paddles communicating with the exterior ofthe cylinder, at least one gas burner arranged below the cylinder todirect flame into the interior of the hollow paddles, said cylinderbeing surrounded along its length by a cylindrical wall defining acombustion space between said cylinder and said wall communicating withthe interior of said paddles and the bottom thereof being open to saidburner, the top of the combustion space including a tapered flue gascollection manifold which communicates with a flue duct for removingwaste combustion gases, and means for introducing air into saidcylinder, said means com prising a passageway for conducting ambient airaround said cylinder to preheat the air and for separating the ambientair from combustion gases, a fan for drawing air through said passagewayand ducting for the preheated air to the interior of said cylinder.

8. A rotary drier as claimed in claim 7 further including an inlet probefor introducing pre-heated air into said cylinder at a positionintermediate its ends.

1. A rotary drier for particulate or loose material comprising acylinder arranged to rotate about its axis inclined to the horizontal,said cylinder having formed along its cylindrical surface a plurality ofhollow paddles extending axially along said cylinder and inwardlythereof, said paddles being V-shaped in cross section with one side ofeach paddle being disposed radially and the other side being disposedobliquely thereto, the interior of said paddles communicating with theexterior of the cylinder and at least one gas burner arranged below thecylinder to direct flame into the interior of the hollow paddles.
 2. Arotary drier as claimed in claim 1 in which said burner comprises aplurality of strip burners which are provided positioned obliquely withrespect to the cylinder axis.
 3. A rotary drier as claimed in claim 1 inwhich said cylinder is surrounded along its length by a cylindrical walldefining a combustion space between said cylinder and said wall, theinterior of said paddles communicating with said combustion space, andthe bottom of the combustion space being open to said burner.
 4. Arotary drier as claimed in claim 3 in which the top of the combustionspace includes a tapered flue gas collection manifold which communicateswith a flue duct for removing waste combustion gases.
 5. A rotary drieras claimed in claim 4 further including means for introducing air intosaid cylinder, said means comprising a passage way for conductingambient air around said cylinder to preheat the air and for separatingthe ambient air from combustion gases, a fan for drawing air throughsaid passage way and ducting for passing the preheated air to theinterior of said cylinder.
 6. A rotary drier as claimed in claim 5further including an inlet probe for introducing pre-heated air intosaid cylinder at a position intermediate its ends.
 7. A rotary drier forparticulate or loose material comprising a cylinder arranged to rotateabout its axis inclined to the horizontal, said cylinder having formedalong its cylindrical surface a plurality of hollow paddles extendingaxially along said cylinder and inwardly thereof, the interior of saidpaddles communicating with the exterior of the cylinder, at least onegas burner arranged below the cylinder to direct flame into the interiorof the hollow paddles, said cylinder being surrounded along its lengthby a cylindrical wall defining a combustion space between said cylinderand said wall communicating with the interior of said paddles and thebottom thereof being open to said burner, the top of the combustionspace including a tapered flue gas collection manifold whichcommunicates with a flue duct for removing waste combustion gases, andmeans for introducing air into said cylinder, said means comprising apassageway for conducting ambient air around said cylinder to preheatthe air and for separating the ambient air from combustion gases, a fanfor drawing air through said passageway and ducting for the preheatedair to the interior of said cylinder.
 8. A rotary drier as claimed inclaim 7 further including an inlet probe for introducing pre-heated airinto said cylinder at a position intermediate its ends.